Thuy, you do not need a separate gateway definition for an interface with a default gateway.
An example of the need for a static gateway route would be when you have, for example, Internal=10.10.10.1/24 and there's a router at 10.10.10.2 behind which is the network 10.10.20.0/24. In this case, you need a static route in the UTM '10.10.10.20/24->10.10.10.2'.
Thuy, you do not need a separate gateway definition for an interface with a default gateway.
An example of the need for a static gateway route would be when you have, for example, Internal=10.10.10.1/24 and there's a router at 10.10.10.2 behind which is the network 10.10.20.0/24. In this case, you need a static route in the UTM '10.10.10.20/24->10.10.10.2'.